This invention relates to an expansion valve operated by a motor.
An expansion valve of this type is disclosed, for example, in Japanese Utility Model Disclosure (Kokai) No. 58-9577. In this motor-driven expansion valve, a valve member is threadably mounted concentric with a rotor and, when the rotor is rotated in one or the other direction, the valve member is moved toward and away from a valve seat.
In this motor-driven expansion valve, while the distance between the valve member and the valve seat is kept constant with the rotor at a standstill, the flow of a coolant through the valve seat varies in its direction to cause a variation of the coolant pressure which is loaded onto the valve member. In this case, the valve member is somewhat displaced relative to the valve seat due to a clearance in the threaded portion of the rotor and valve member. That is, when the coolant flows through the valve seat in one or the other direction, the same distance is not obtained between the valve member and the valve seat even if the output shaft of the motor has the same rotational angle. It is therefore not possible to precisely control the coolant flow when the coolant in the motor-driven expansion valve flows in one or the other direction.
This type of a motor-driven expansion valve is also disclosed in Japanese Patent Disclosure (Kokai) No. 57-186681. In this motor-driven expansion valve, a rotational force is transmitted from the output shaft of the motor through a gear train to the output shaft of the gear train. In a valve casing including fluid passages and valve seat, a valve member is threaded to the valve casing such that it is in alignment with the output shaft of the gear train. A hole of a square cross-sectional configuration is formed at the rotational center of that end face of the valve member which is remote from the valve seat. The output shaft of the gear train which has a corresponding square cross-sectional area is inserted through the hole of the valve member. When the valve member is rotated in one or the other direction through the output shaft of the gear train, the valve member is moved toward and away from the valve seat, while at the same time the inner wall face of the valve member hole is slidable relative to the output shaft of the gear train along the longitudinal axis of the output shaft of the gear train.
In the motor-driven expansion valve of Japanese Patent Disclosure (Kokai) No. 57-186681, it is necessary to make the length of the output shaft of the gear train and depth of the hole of the end face of the valve member longer than the distance over which the valve member is moved and it is also necessary to make the longitudinal axes of the output shaft and said hole coincide with design-predictable rotational axes thereof. Thus, the greater the distance of the movement of the valve member, that is, the greater the length of the output shaft of the gear train and depth of the hole of the end face of the valve member, the more difficult it is to make the longitudinal axis of the output shaft of the gear train coincide with a design-predictable output shaft of the gear train and the more difficult it is to make the longitudinal axis of the hole in the end face of the valve member coincide with a design-predictable longitudinal axis of the hole. Such a difficulty in manufacture also involves a higher cost.